Methane and Vets

The attendees at the recent New Zealand Veterinary Conference in Wellington had the opportunity to hear a masterly review  on “Methane and efficiency of productions- a vet’s guide to making a difference” by Professor Ian Lean of Sydney University. Below I have summarised some of the main points from this presentation.

The lecture opened with the history of carbon emissions which have, of course, risen rapidly since the widespread utilisation of fossil fuels over the last few hundred years. Professor Lean confirmed that emissions of greenhouse gases from cattle, particularly methane, do have significant global warming impact but emphasised that these are biogenic in nature, part of a closed carbon cycle involving plants, soil and atmosphere as well as animals. Hristov has estimated that historical emissions from bison and deer in the USA may have been 84% of current emissions. He added that cattle and sheep frequently consume foods which are inedible to humans or are by products of human food production. 

Professor Lean continued by stating that, all too frequently, the popular view is based on ideological, simplified information rather than robust scientific data. The need for quality, evidence based evaluation has never been greater. And dairy cattle are the third largest source of proteins and fats in human diets, reminded Professor Lean.

Different countries have differing agricultural systems so that in New Zealand, for example, dairying emits almost 50% of agricultural emissions whereas in Australia the picture is different, and grazing beef represents the biggest agricultural emitter.

Professor Lean emphasised the importance of intensity of emissions, showing a slide that plotted, for a range of countries, the  milk yield per cow against the carbon footprint linked to production. New Zealand’s pasture based system has one of the lowest carbon footprints but production per cow is also low when compared to  countries like the USA, Canada or Sweden where production per cow is more than twice as high for a similar carbon footprint. There is a simple relationship between milk production and the intensity of methane emissions and this can be demonstrated by dietary calculation.

There is certainly room to improve and Professor Lean reviewed a number of routes by which the carbon footprint of cattle farming might be reduced. These include genetic selection, feed modification, (including ionophores, seaweed and 3-NOP,) and improving reproductive performance. This latter opportunity can involve initiatives to source more calves for rearing from dairy and also calving heifers at a younger age. 

Comparing more intensive dairying systems like Australia’s where cows consume significant quantities of by-products (on average 1.6 tonne per cow per year) to traditional pasture systems, demonstrates the higher milk yield/ lower foot print relationship; Professor Lean commented that his preference was towards increasing the intensity of production systems. But farming systems, including manure management, must be fully evaluated using a science based approach. Housing for example can increase dry matter intake and save energy lost in walking to and from paddocks. And utilising by-products is important: 4 Kg by-products are produced for each Kg of vegan food, he reminded us, with his tongue perhaps slightly protruding from his cheek!

In conclusion, he stated that there is definitely a role for the profession to be involved in reducing the carbon footprint of the dairy industry, stating that 0.4% per annum was achievable and that, were this to be achieved, cows could be viewed as having a cooling effect on the planet.